var _ = function(selector){
    // 返回个元素
    if(selector.indexOf('.')!=-1){
        // var aa=selector.indexOf('.');
        // selector=selector.slice(aa);
        return document.getElementsByClassName(selector.slice(1));
    } else if(selector.indexOf('#')!=-1) {
        // var bb=selector.indexOf('#');
        // selector=selector.slice(bb);
        // console.log(selector);
        return document.getElementById(selector.slice(1));
    } else {
        return document.getElementsByTagName(selector);
    }
    
}